KR102243405B1 - Additives for improving the ionic conductivity of lithium-ion battery electrodes - Google Patents

Abstract

The present invention relates to an electrode material for a lithium ion battery, preferably a positive electrode material, a method of manufacturing the above, and a lithium ion battery incorporating the electrode material. The composite electrode material includes:
-Electrically conductive additives such as carbon;
-Active substances which are oxides, phosphates, fluorophosphates or silicates of lithium;
-Polymeric binders such as PVDF; And
-Organic salts corresponding to the specified chemical formulation, for example LiPDI, LiTDI, LiPDCI, LiDCTA, LiFSI, LiTFSI (optionally as a mixture).
Organic salts make it possible to increase the ionic conductivity of the electrode.

Description

Additives for improving the ion conductivity of lithium-ion battery electrodes {ADDITIVES FOR IMPROVING THE IONIC CONDUCTIVITY OF LITHIUM-ION BATTERY ELECTRODES}

The present invention relates generally to the field of electrical energy storage of lithium storage batteries of the Li-ion type. More specifically, the present invention relates to a Li-ion battery electrode material, a method of making the same, and its use in Li-ion batteries. Another subject matter of the present invention is a Li-ion battery manufactured by incorporating the electrode material.

Li-ion storage batteries or basic cells of lithium batteries are generally made of lithium metal or carbon based anodes (when discharged) and lithium intercalating compounds of the generally metal oxide type, such as LiMn ₂ O ₄ , LiCoO ₂ or LiNiO ₂ It includes a cathode made of (likely, when discharging), between which an electrolyte that conducts lithium ions is inserted.

In use, therefore, during the discharge of the battery, ^{the lithium released by oxidation at the negative pole by the anode in the ionic form Li +} moves through the conductive electrolyte and in the crystal lattice of the active material of the cathode (+) pole. Will be inserted by the reduction reaction of. ^{The passage of each Li +} ion in the internal circuit of the battery is precisely compensated by the passage of electrons in the external circuit. It generates an electric current that can be used to supply the equipment.

Upon charging, the electrochemical reaction is reversed, and lithium ions are released by oxidation at the (+) pole, the “cathode” (the cathode at discharge becomes the anode upon recharging), and they are released from it via the conductive electrolyte. Moving in the reverse direction (where they circulate during discharging), negative poles, "anode" (likely, the anode at discharging becomes the cathode upon recharging) will be deposited or inserted by reduction at this time They can form dendrites of lithium metal, which are possible causes of short circuits.

The cathode or anode generally comprises one or more current collectors deposited with a composite material consisting of: one or more "active" substances (which are active because they exhibit electrochemical activity towards lithium), which act as a binder and generally Functionalized or non-functionalized fluoropolymers such as polyvinylidene fluoride, or aqueous-based polymers of the carboxymethylcellulose type, or at least one polymer which is a styrene/butadiene latex, plus at least one electron-conducting additive (typically Is an allotropic form of).

Conventional active materials in the negative electrode are generally lithium metal, graphite, silicon/carbon composites, silicon, _{fluorographite of type CF x} (x is 0 to 1) and titanate of type _{LiTi 5} O _12.

Conventional active materials in the positive electrode are generally LiMO ₂ type, LiMPO ₄ type, Li ₂ MPO ₃ F type, Li ₂ MSiO ₄ type (where M is Co, Ni, Mn, Fe or a combination thereof), LiMn ₂ O ₄ type or S ₈ type.

Recently, additives have been used that make it possible to improve the permeability of the electrolyte to the core of the electrode. As a result of the growing demand for high energy batteries, ie batteries with higher electrical storage capacity, the thickness of the electrode is increasing and thus the permeability of the electrolyte is becoming important for the overall resistivity of the battery. For the purpose of improving the permeability, patent WO2005/011044 describes the addition of "inorganic" fillers of metal oxides such as _{Al 2} O ₃ and SiO _2.

These inorganic fillers are added during conventional manufacturing methods of electrodes. The conventional method consists of mixing different components in a solvent or mixture of solvents such as, for example, N-methylpyrrolidone, acetone, water or ethylene carbonate.

a) at least one conductive additive in a content range of 1 to 5% by weight, preferably 1.5 to 4% by weight or 1 to 2.5% by weight, preferably 1.5 to 2.2% by weight, relative to the total weight of the composite material;

b) lithium oxide, phosphate, fluorophosphate or silicate as an electrode active material capable of reversibly forming an intercalating compound with lithium, having an electrochemical potential greater than 2V for the Li/Li ^{+ pair;}

c) polymeric binder.

Then, the obtained ink is coated on the current collector, and the solvent or solvents are evaporated by heating in the range of 30 to 200°C.

The drawback of these inorganic fillers is that they reduce the capacity of the battery by reducing the amount of active material in the electrode, but also only these fillers make it possible to improve the macroscopic diffusion of the electrolyte.

In fact, in the electrode, it is the charge resistance of the active material/electrolyte interface that limits the performance of the battery. The resistance is a microscopic effect that cannot be improved by the addition of macroscopic inorganic fillers.

Applicants have found that the addition of salts consisting of organic anions selected to have desirable interactions on the surface of the active material makes it possible to increase the ionic conductivity of the electrode.

The present invention relates firstly to the use of organic salts as ion conductive additives in the formulation of electrodes of Li-ion storage batteries, preferably in cathode formulations. These salts can also be used in the formulation of electrodes of Na-ion batteries.

Another subject matter of the present invention is the use of the formulation as a battery electrode.

The ion-conducting additive must be able to withstand the conditions of the method for manufacturing the electrode described above. _{For example, LiPF 6} , a lithium salt currently used in most electrolytes, cannot be used as an ion conductive additive due to instability to nucleophilic solvents and temperature instability.

The invention also relates to a Li-ion battery electrode composite material, preferably a positive electrode material, comprising:

a) at least one electron-conducting additive in a content range of 1 to 5% by weight, preferably 1.5 to 4% by weight or 1 to 2.5% by weight, preferably 1.5 to 2.2% by weight, relative to the total weight of the composite material;

b) lithium oxide, phosphate, fluorophosphate or silicate as an electrode active material capable of reversibly forming an intercalating compound with lithium, having an electrochemical potential greater than 2V for the Li/Li ^{+ pair;}

c) polymeric binders;

d) at least one organic salt of formula A and/or B:

In formula (A), -X _i - to the group independently represents an atom ^{or: -N =, -N - -,} -C (R) =, -C - (R) -, -O-, -S (=O)(R)= or -S(R)=, R is F, CN, NO ₂ , S-CN, N=C=S, -OC _n H _m F _p , -C _n H _m F _p (n, m and p are integers) represents a group selected from. Particularly preferred compounds of formula (A) are imidazolates shown below, advantageously lithium imidazolates:

[In the formula, R represents F or -C _n H _m F _p ]. These lithium salts are particularly advantageous because of their insensitivity to water, which makes possible simple use in the manufacturing method of the electrode.

In formula (B), R _f is F, CF ₃ , CHF ₂ , CH ₂ F, C ₂ HF ₄ , C ₂ H ₂ F ₄ , C ₂ H ₃ F ₂ , C ₂ F ₅ , C ₃ F ₆ , C ₃ H ₂ F ₅ , C ₃ H ₄ F ₃ , C ₄ F ₉ , C ₄ H ₂ F ₇ , C ₄ H ₄ F ₅ , C ₅ F ₁₁ , C ₃ F ₅ OCF ₃ , C ₂ F ₄ OCF ₃ , C ₂ H ₂ F ₂ OCF ₃ or CF ₂ OCF ₃ , Z represents an electron withdrawing group selected from F, CN, SO ₂ R _f , CO ₂ R _f or COR _f.

In the above general formula, M ⁺ represents a lithium cation, sodium cation, quaternary ammonium or imidazolium.

Preferably, component (d) can vary from 0.01 to 10% by weight, advantageously from 0.05 to 5% by weight, relative to the total weight of the material.

The polymeric binder is advantageously selected from functionalized or non-functionalized fluoropolymers such as polyvinylidene fluoride (PVDF), or aqueous-based polymers of the carboxymethylcellulose type or styrene-butadiene latex.

The electron-conducting additive is preferably selected from conductive organic polymers or different allotropic forms of carbon.

Manufacture of electrodes

Another subject matter of the present invention is a method for preparing the electrode composite material described above, comprising:

i) a step for preparing a suspension comprising at least:

-One or more organic salts of formulas A and/or B;

-Electron-conducting additives;

-Polymer binders;

-One or more volatile solvents;

-An electrode active material selected from lithium oxide, phosphate, fluorophosphate or silicate, and

ii) The step of producing a film, starting from the suspension prepared in (i).

The suspension can be obtained in any mechanical manner, for example by means of a rotor-stator or anchor stirrer, or by dispersion and homogenization by means of ultrasonic waves.

The suspension is optionally from polymers in the pure state or in the form of solutions in one or more volatile solvent(s), organic salts in the pure state or in the form of suspensions in one or more volatile solvent(s), electron-conducting additives and active substances in the pure state. Can be prepared after the drying step at a temperature of 50 to 150 ℃.

Preferably, the volatile solvent(s) is selected from organic solvents or water. In particular, organic solvents N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO) may be mentioned as the organic solvent.

Suspensions can be prepared in a single step, or in two or three successive steps. When the suspension is prepared in two successive steps, one embodiment is to prepare a dispersion containing all or part of a solvent, organic salt(s) and optionally a polymeric binder in the first step using a mechanical method, and then It consists in adding other components of the composite material to the first dispersion in a second step. The film is then obtained from the suspension at the end of the second step.

When the suspension is prepared in three successive steps, one embodiment is to prepare a dispersion containing all or part of an organic salt(s) in a solvent and optionally a polymeric binder in the first step, followed by the second step. It consists in adding the active substance and removing the solvent to obtain a powder, and then adding the solvent and the remainder of the components of the composite substance to obtain a suspension. The film is then obtained from the suspension at the end of the third step.

Dissolution of the organic salts of formulas A and/or B can be carried out at a temperature in the range of 0 to 150°C, preferably 10 to 100°C.

Another subject matter of the present invention is the use of one or more organic salts of formulas A and/or B as ion conductive additives in the manufacture of electrode composite materials.

Additionally, the subject matter of the present invention is a Li-ion battery incorporating the above material.

Example 1:

Stirring is carried out using a rotor-stator. 0.0197 g of LiTDI (formula above) is placed in the flask. Dissolution is carried out with 7.08 g of NMP, and the solution is left to stir at 25° C. for 10 minutes. Adding a PVDF (Kynar ^®) of 0.1974 g and was placed and the mixture was stirred at 50 ℃ for 30 minutes. Then 0.1982 g of Super P carbon (Timcal®) are added and the mixture is left to stir for 2 hours. Finally, 4.5567 g of LiMn ₂ O ₄ and 2.52 g of NMP are added, and the mixture is left to stir for 3 hours. Subsequently, the suspension is diffused on an aluminum sheet in the form of a film having a thickness of 100 μm. The film is dried at 130° C. for 5 hours.

Example 2:

Stirring is carried out using a rotor-stator. 0.0212 g of LiTDI is placed in the flask. Dissolution is carried out with 2.84 g of NMP, and the solution is left to stir at 25° C. for 10 minutes. Adding a PVDF (Kynar ^®) of 0.1063 g and was placed and the mixture was stirred at 50 ℃ for 30 minutes. Then, after addition of 0.1059 g Super P carbon (Timcal ^®), and puts the mixture was stirred for 2 hours. Finally, 4.5580 g of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and 4.52 g of NMP are added, and the mixture is allowed to stir for 3 hours. The suspension is spread on an aluminum sheet in the form of a 250 μm thick film. The film is left to dry at 130° C. for 8 hours.

Claims (10)

Battery electrode composite material, comprising:
a) at least one electron-conducting additive in a content range of 1 to 5% by weight, or 1.5 to 4% by weight or 1 to 2.5% by weight, or 1.5 to 2.2% by weight, relative to the total weight of the composite material;
b) lithium oxide, phosphate, fluorophosphate or silicate as an electrode active material capable of reversibly forming an intercalating compound with lithium, having an electrochemical potential greater than 2V for the Li/Li ^{+ pair;}
c) polymeric binders;
d) at least one organic salt of formula A:

_[I -X in formula A - is independently a group or atom ^{represents: -N =, -N - -,} -C (R) =, -C - (R) -, -O-, -S (= O)(R)= or -S(R)=, R is F, CN, NO ₂ , S-CN, N=C=S, -OC _n H _m F _p and -C _n H _m F _p (n , m and p are integers); And M ⁺ represents lithium, sodium, quaternary or imidazolium cation, and the compound of formula A is imidazolate]. The battery electrode composite material according to claim 1, wherein the compound of formula A is lithium imidazolate. The battery electrode composite material according to claim 1, wherein the organic salt(s) represents 0.01 to 10% by weight, or 0.05 to 5% by weight, based on the total weight of the material. The battery electrode composite material of claim 1, wherein the polymeric binder is selected from fluoropolymers, water-based polymers or styrene/butadiene latexes. The battery electrode composite material of claim 1, wherein the electron-conducting additive is selected from conductive organic polymers or different allotropic forms of carbon. A method of manufacturing a battery electrode composite material according to any one of claims 1 to 5, characterized in that it comprises:
i) a step for preparing a suspension comprising at least:
-At least one organic salt of formula A;
-Electron-conducting additives;
-Polymer binders;
-One or more volatile solvents;
-An electrode active material selected from lithium oxide, phosphate, fluorophosphate or silicate, and
ii) The step of producing a film, starting from the suspension prepared in (i). 7. The process according to claim 6, characterized in that the volatile solvent(s) is selected from organic solvents and water. 8. The method of claim 7, wherein the organic solvent is selected from N-methylpyrrolidone or dimethyl sulfoxide. Li-ion battery comprising the battery electrode composite material according to any one of claims 1 to 5. delete